The present invention relates generally to a method of circular patterning, and more particularly to a method of circular patterning which obtains a stable circular pattern or island without being affected by a difference in minute shapes of masks used for etching.
Prior art exposure devices such as mask aligners transfer a mask pattern to a photoresist layer on a substrate by contacting a chrome mask formed on glass (hereinafter referred to as a glass mask or simply a mask) with the substrate. The transferring process is commonly referred to as a photo fabrication process. Because of this, the shape of the mask is transferred to the photoresist layer with high accuracy.
For example, in FIGS. 8 to 10, the prior art etching processes are shown. Each of FIGS. 8A, 9A, and 10A shows a sectional view of the process and each of FIGS. 8B, 9B, and 10B shows a plane view thereof. As shown in FIG. 8A, silicon oxide film (SiO.sub.2) 22 is formed on a silicon substrate 20 by thermal oxidation or the like, and a photoresist film is applied thereon.
Next, resist masks 24a shown in FIGS. 9A and 9B are formed on the silicon oxide film 22 by transferring the mask patterns to the photoresist 24 by a photolithography technique using the above-mentioned exposure device such as a mask aligner. Here, circular and rectangle resist masks are formed as resist masks 24a.
In FIG. 10, a desired pattern 22a is obtained by the silicon oxide film 22 using, for example, buffered hydrofluoric acid solution (BHF) or the like using the resist mask as an etching mask.
However, when the configuration of the circumference of the mask pattern itself is uneven and the shape thereof is distorted when comparing it with a plan diagram, the prior art etching process transfers a mask pattern including these problems because the mask pattern is transferred with high accuracy.
It is difficult to repair a defect at an end process in the prior art etching process.
In the above-mentioned mask, a reproduction of an original mask is generally used by producing an original mask by drawing on the mask after transformation of a coordinate system shape drawn by CAD or the like. Because of this, although high accuracy of transformation of the coordinate system is achievable for overcoming unevenness of the configuration of the circumference portion and the distorted shape of the above-mentioned mask pattern, transformation of the coordinate system can not entirely repair the defect and a high cost for the mask becomes inevitable.
As a defect in the mask pattern appears more often in a curved line pattern such as a circle than in a linear pattern such as a rectangle, a method of forming an accurate circular pattern is required.
Moreover, a defect in pattern shape sometimes appears due to a cause other than the mask shape, for example, because of dirt and dust infiltration during the fabrication process.
The present invention was made with regard to above-mentioned drawbacks of the prior art. An object of the present invention is to provide a method of processing a circular pattern enabling a desired circular pattern to be obtained even if there is pollution caused by dirt and/or dust or a defect in the mask pattern.